In recent years, owing to developments in the technology for compressively coding audio or video, increases in the performance of personal computers (PC) and the spread of the Internet, the so-called streaming service has been generalized. In the streaming service, audio or video data on the network are accessed and played back while being received. In order to receive the streaming service, an apparatus or a software program for receiving and playing back the data is required. At the present time, it is mainstream that a data playing software is activated on a PC to receive and play back audio or video data.
As the compressive coding method, many methods are used at present, such as MPEG-1, MPEG-2 and MPEG-4, which are standardized by ISO/IEC, and H.261, H.263 and G.729, which are standardized by ITU-T. When playback software on a PC does not support the compressive coding method for audio or video data which are included in accessed data, the playback software can analyze decoding software information which is added to the accessed data, and download the decoding software on a network to automatically incorporate the decoding software into the playback software. Accordingly, the data according to various kinds of compressive coding methods can be decoded.
To determine a file format in a case where audio and video is to be multiplexed, the extension of the file (a character string normally composed of three alphanumeric characters situated after a “.” (dot) behind the file name) is usually used. The PC can also handle the file format flexibly. For example, the same data playback software supports plural file formats, or data playback software programs are switched for each file format.
As described above, flexible structures having greater extensibility are possible on the PC.
Recently, portable terminals (portable telephones) have remarkably come into wide use. Further, the portable terminals are frequently provided with new functions. In the so-called “I-mode” services which were started in 1999, the connection of the portable terminals with the Internet become possible. It is also expected that digital data including audio and video on the Internet can be accessed from the portable telephones to receive and play back the data, in the near future.
However, it is difficult for the portable telephone to have a flexible and extensible structure like the playback software in the conventional PC. One reason is that the portable terminal is required to be compact to allow the user to carry it with him. Therefore, the portable terminal is forced to support only extremely limited compressive coding methods or file formats, and thus it is important to judge whether or not a compressively coded format or file format can be played back on the portable terminal side.
Even when extensions of file formats are the same, there could be some cases where the data can be played back by the PC, while the data cannot be played back by the portable telephone. This is due to restrictions on the hardware of the portable telephone or the software. Therefore, there are some cases where it cannot be simply judged only from the file format whether or not the playback can be performed.
Further, as in the case of I-mode, the portable terminal can also access data on common Internet servers. As an example of the methods for accessing the Internet servers, there is a capability switching method for previously judging whether or not data which are to be received can be decoded and played back by the portable terminal before starting to receive the data, and thereafter receiving the data only when the decoding and playback of the data is possible. However, this capability switching method has not become widespread on the common Internet servers, and cannot be used generally. Thus, it cannot be put to practical use under the present circumstances in which portable terminal is controlled by using the capability switching method to receive the data only when the decoding and playback is possible.
Further, in the case of portable terminals, the communication charges are higher than those of the common Internet connection, and the communication charges are further added according to the quantity of received data, whereby data receiving should be stopped immediately when the data playback is impossible. However, the conventional portable terminal has no means for enabling this.